Our client, a multi-national oil and gas company, operated a site that was part of our environmental liability transfer portfolio that we managed for them. This site had been utilized since the early 1960s as a gasoline filling station. The client no longer owned the property but was identified by the state's department of natural resources as the responsible party for a leak incident from historic underground storage tanks.
Significant subsurface soil impacts were located in close proximity to vapor receptors. The state's department of natural resources required an evaluation of the receptors to quantify the vapor intrusion risk to each individual receptor.
An adjacent motel, which is listed on the National Register of Historic Places, complained of petroleum vapors in the basement.
Characterization was expedited through the use of enhanced data visualization, which provided statistical data interpolation and 4-dimensional geophysical modeling as the foundation of an enhanced conceptual site model.
To evaluate the vapor intrusion pathway at the site, numerous soil vapor monitoring points were installed in areas of high soil impacts and in areas of suspected preferential migration pathways.
The basement drain of the motel was rerouted out of areas of known soil impacts and the previous piping plugged. A sub-slab depressurization system was installed as a safeguard.
Additional soil and soil vapor delineation discovered an unknown orphan UST system and an area of Light Non-Aqueous Phase Liquid (LNAPL) unrelated to the client’s former site in close proximity to the motel.
Evaluation of the results visualization model results provided validation of geological conditions, which supported that the soil vapor pathway at the site was not complete.
The state department of natural resources identified a recommended practice (RP) for the orphan UST system and has required further investigation of their impacts. The client’s past site is on track for closure in early 2020.